Here is a picture of the basic Zoom screen. When you connect to Zoom, this is NOT the exact image you will see.
You will see yourself, probably your professor, and likely some of your classmates. (Names will appear if the user has stopped their video.)
You should see the bottom part of the screen (called the tray). Here you might see a number of options, including Mute, Stop Video, Security, Participants, Chat, Share Screen, Record, and Reactions.
There is also an option to Leave - this will disconnect you from the class.
To Exit or Enter full screen, see the option at the upper right.